The private detective had also provided me with a contact number where I could organize an ESDA test on the paper on which the letter had been written. By then it must have been obvious that I had no funds to pay him for investigative services, and perhaps he realized he had nothing to lose by offering me the details. Routine and dull as it might be, checking up on unfaithful lovers was going to continue paying the bills, whereas I, as he had probably guessed from the start, was on a long quest with no certainty of finding an answer.

There was one very important element that I had not yet considered, though it was potentially full of clues: the bottle. The choice of vessel, its origin, its image, its date of manufacture – all this information could be of use. I decided to ring the mineral water company, Evian.

It was obvious from the most cursory research on the internet that Evian belonged to the Danone Corporation. The English headquarters promised to call back with information on the bottle but did not, so I decided to ring the ‘24-hour Evian telephone consumer service’. ‘Delphine’ took the call but was, perhaps understandably, reluctant to listen to the details. It was far removed from the kind of questioning for which she had been trained, and I was not interested in how many years the water had been filtered ‘through pristine glacial rock formations in the French Alps’. It turned out to be fifteen years.

She was inclined to be dismissive of my query, but when I persisted, describing the beauty of the bottle, she told me that this type of container had first been released in limited numbers for the Albertville Winter Olympic Games of 1992. Its success was such that it was relaunched as the Millennium Bottle in late 1999. According to the company website, ‘This pure and perfect form is the very symbol of water.’ Since then, by public demand, it had been re-released every year. As many as 400,000 of these bottles were in circulation. I mentioned that the one in question had 20-02 engraved on it. Wouldn’t that narrow down the field? She conceded the point, though somewhat reluctantly.

No, I could not bring the bottle in to ask for any more information. No, visitors were not allowed at the Evian factory. I pointed out that I was not attacking Evian; on the contrary, someone had thought their bottle a suitable vessel for the most important letter of her life. Finally she agreed to pass the message upwards and promised me that someone would return my call.

The Director of External Relations for Danone rang back and left a message on my machine. ‘We are not particularly interested in your little story of a bottle on the beach,’ she said in a tone of the most superior scorn and disdain. ‘But if you want to ring me, I’m on . . . ’ and she rattled off a number full of reversed 80s and 90s in the speediest French possible, which took me eighteen message replays to decipher. Four-twenty-five, four-twenty-eleven, fifty-two, four-twenty-ten-seven, twenty-six, four-twenty-five, four-twenty-eleven, fifty-two, four-twenty-ten-seven, twenty-six. Finally I worked out that she had repeated her number twice on the message but without drawing breath in between. I gritted my teeth and realized I had to try to win her over in order to secure vital clues about the bottle.